Acoustical tile construction



March 23, 1965 K. w. SCHULZ ETAL 3,174,580

YACOUSTICAL TILE consmucnon Filed April 28, 1961 l6 l6 INVENTORS Carl 6.Schulz United States Patent 3,174,580 ACOUSTICAL TILE CQNSTRUCTION KurtW. Schulz, 908 Dawes Ave, and Carl G. Schulz, 1314 Oneida, both ofJuliet, Ill. Filed Apr. 28, 1961, Ser. No. 106,270 2 Claims. ('Cl.181-33) This invention relates generally to acoustical tile and moreparticularly to acoustical tile having one surface provided with apattern of sound receiving recesses.

It is an object of the present invention to provide a novel acousticaltile which because of its construction has a higher noise reductioncoetficient than that of conventional acoustical tile. Moreparticularly, it is an object to provide an acoustical tile which notonly absorbs and thereby dampens sound vibrations, but also effectivelytraps within it a portion of the vibrations which strike it.

An ancillary object is to provide such an acoustical tile which readilypermits sound vibrations to enter its sound receiving recesses and theneffectively prevents escape of the vibrations out of the recesses.

It is an additional object to provide an acoustical tile having asurface which due to its novel construction is both stronger and moreatttractive than the facing of ordinary acoustical tile.

Yet another object is to provide a novel acoustical tile having theabove characteristics which is inexpensive and economical tomanufacture, easy to install and which may be readily and convenientlycleaned or painted.

Other objects and advantages of the invention will become apparent uponreading the attached detailed description land upon reference to thedrawings in which:

FIGURE 1 is a perspective view showing an illustrative acoustical tileincorporating the features of the present invention;

FIG. 2 is an enlarged fragmentary perspective view of a corner portionof the tile; and

FIG. 3 is an enlarged fragmentary cross-sectional view taken along theline 33 in FIG. 1.

While the invention will be described in connection with a preferredembodiment, it will be understood that we do not intend to limit theinvention to that embodiment, but on the contrary, intend to coveralternatives, modifications and equivalents as may be included withinthe spirit and scope of the invention as defined by the appended claims.

Turning now to the drawings, there is shown an acoustical tileincorporating the features of the present invention. In the preferredembodiment, thetile 19 comprises a substantially flat, relatively thinfacing sheet 11 and a thick, substantially rigid backing board 12. Itwill be understood that the backing board 12 is made of any suitablefibrous or composition material commonly employed in the fabrication ofconventional acoustical tiles. The light-weight, porous nature of suchmaterials has made them particularly well suited for acoustical endusessince their sound absorbing properties greatly exceed those ofnon-porous materials.

As shown (see especially FIG. 3), the backing board 12 has a rearsurface 13 and a front surface or face 14. To lend sound absorbingefiiciency to the backing board 12 it is provided with a plurality ofsound absorbing recesses or openings which extend from the face 14substantially into but not entirely through the thickness of the board.In this instance the recesses 15 are substantially circular incross-section and are each defined by a circumferential wall 16terminated by a circular base 17. As is well know such recesses functionto permit ready dispersion throughout the board of sound vibrationswhich strike its front surface.

3,174,580 Patented Mar. 23, 1955 ice Such a backing board 12 may beprepared, for example, by cutting a suitable insulating type fiber boardto the desired size, eg 12" x 12" x /4", and drilling its front face 14using a single or multiple spindle drill to provide the plunality ofrecesses 15 extending from the front face 14 of the tile toward its rearsurface. An exemplary pattern of recesses in such a tile would bediameter holes drilled on /2" centers to form 22 rows of 22 holes eachor 484 holes in each tile. Alternatively, an irregular pattern of holesof uniform or varying diameters may be employed if desired.

The facing sheet 11 is preferably formed of relatively thin metal, rigidplastic sheeting or the like, and is provided with a plurality of soundreceiving openings or holes 18 which openings are of the same shape asand arranged in the same pattern as that chosen for the recesses 15provided in the backing board 12.

As will be seen the facing sheet 11 is juxtaposed in relation to thebacking board 12 such that the centers of the openings 18 register withthe centers of the recesses 15. The sheet 11 and backing board 12 may besecured together in any suitable manner, for example by using a suitableadhesive. As shown the edges of the facing sheet 11 are flashed aroundthe peripheral edges of the backing board. Preferably a marginal edgeportion 20 of the facing sheet 11 is folded or crimped rearwardly aroundthe edge of the backing board 12, the shape of the board edge and edgeportion 20 being such as to define an apex 21 as viewed in section whichforms a line of juncture between adjacent tiles when they are assembledtogether.

A peripheral groove 24 is preferably provided around the sides of theboard and positioned rearwardly of the edge portion 20 for receiving theflange of an I-bar or T-bar (not shown) attached to the ceiling or wallto which the tile is to be secured, or for receiving a suitable spline(also not shown) which facilitates alignment of and strengthens adjacenttiles. In order to accom modate the web of such an I-bar or T-bar therearmost portions 220, 23a of the cojoining sides 22, 23 are formed soas not to extend outwardly as far as the plane of the line of juncturebetween tiles defined by the apex 21. When the illustrative acousticaltiles are so installed the grooves 24 of adjacent tiles accommodate theflange of the beam passing between them with the web of the beam beingreceived between the adjacent side portions 22a, 23a of the tiles.

The bevelled corner 26 of the backing board 12 peripherally surroundingthe face 14 improves the interfit of adjacent tiles as well as theirappearance. In this way the facing sheet 11 is made to conformintimately to the outer surface 14 of the backing board 12, therebyproviding a neat and attractive acoustical tile.

The sound absorbing efficiency of acoustical tile, of course, variesdepending on a number of factors including its thickness, porosity, andthe depth, diameter and pattern of the recesses 15. The sound absorbingefiiciency of a given tile is evaluated by those skilled in this art bya standard test which determines the noise reduction coefiicient (NRC)of the material. This test consists of measuring the reverberation roomsound absorption efficiency of the tile at a series of fixed soundfrequencies, i.e. at 250, 500, 1,000 and 2,000 cycles per second. Thearithmetic average of the reverberation room sound absorptioncoefficients at each frequency becomes the overall noise reductioncoefficient. The average noise reduction coefficient of conventionalacoustical tile often varies in the range of .40 to .60. It isunderstood that the higher NRC value designates the better soundinsulator.

In accordance with the present invention, the sound absorbing efficiencyof the acoustical tile is greatly improved as compared with conventionaltiles by making the face sheet openings 18 smaller in diameter than thediameters of the recesses with which they register. Due to thisconstruction the NRC of the instant acoustical tile is much higher thanhas been feasible in the past. As will be seen from the drawings, aportion of sound vibrations which strike the front face of the tile 10will pass through the sound receiving openings 18 in the facing sheet 11and enter the sound absorbing recesses 15 of the board 12. Upon soentering each of the board recesses 15, the sound vibrations strike thewalls 16 and base 17 and become in substantial part absorbed by theporous mass of the backing board 12. The unabsorbed portion of thevibrations are reflected from. these respective surfaces but,importantly, the majority of these vibrations cannot escape from therecesses 15 due to the restriction caused by the smaller diameter of thefacing sheet openings 18 in relation to that of the recesses. It willthus be appreciated that most of the initially unabsorbed portion of theentering sound vibrations are effectively trapped within the soundabsorbing recesses 15 and prevented from escaping out through theopenings 18. The so trapped sound vibrations are subsequently dispersedinto and absorbed by the board proper thereby enhancing the noisereduction efficiency of the tile.

It has been found, moreover, that maximum sound absorbing efficiencyresults when the ratio of the recess (15) diameter to the face sheetopening (18) diameter is in the range of about 1.25 to about 3.33. Insuch instances the acoustical tile of the present invention is found tohave an NRC of as high as 0.75 compared with the usual range of 0.40O.60for ordinary acoustical tile. Table I below sets forth test resultswhich illustrate the improved NRC obtained for acoustical tileconstructed in accordance with the present invention, using differentratios of diameters of the recesses 15 to the openings 13.

The backing board 12 used in all of the instant test t-iles was a oneinch thick commercially available product comp-rising a major proportionof expanded perlite, some vegetable fibers and a minor proportion ofbinder. The facing sheets 11 employed in all test tiles were formed ofthin aluminum sheeting, and the recesses 15 and openings 18 in registrytherewith in all test files were spaced on one half inch centers.

As will be observed from the data in Table l the 1.25 ratio of the twodiameters results in an increased NRC over that obtained using a 1.00ratio, and a ratio of 2.00 or greater provides an even higher NRC.Although no tests were conducted for ratios above 3.33 it is to beexpected that such ratios would result in a further increase in NRC. Asa practical matter, however, it will be appreciated that as the ratio ofdiameters is increased, either the openings 13 in the facing sheet 11become unduly small, thus undesirably restricting the proportion ofimpinging sound vibrations entering them, or fewer recesses 15 may beprovided per square unit of backing board 12. It therefore is desirableto maintain the ratio of recess (15) diameter to opening (18) diameterwithin approximately the above mentioned range, i.e. from about 1.25 toabout 3.33.

For the purpose of increasing the sound trapping effect and also toimprove the strength and appearance of the facing sheet 11, the portionsof the facing sheet 11 marginal to the openings 18 are preferably formedwith an internally extending circumferential lip 19 (see FIG. 3). It isunderstood that the lip 19 may be formed by any convenient method, suchas by first drilling a plurality of holes in the sheet 11 and thenpressing enlarged tapered punches through the holes to stretch and curveinwardly the peripheral stock. In this way each of the openings 18 isprovided with a circumferentially tapered shoulder having a smoothlyrounded contour which merges into the plane of the facing sheet 11. Thelip 19 thereby in cooperation with the recess wall 16 forms a captivecorner which increases the proportion of sound vibrations trapped withinthe recess 15. Such .trapped vibrations are of course eventuallyabsorbed by the board 12. The rearwardly extending lip 19 serves,moreover, to strengthen the relatively thin facing sheet 11 by giving ita' corrugated-like or dimpled construct-ion. The rounded contours of theopenings 18 also impart to the face of the tile a considerably enhancedappearance (see FIG. 1).

It is understood that where reference is made herein to the diameter ofthe openings 18, the diameter meant is the inside diameter at therearmost end 19a of the lip 19 (see FIG. 3). Of course it may under somecircumstances be preferable to form the facing sheet 11 as simply apunched or drilled flat sheet, i.e. Without provision of thecircumferential lips 19 surrounding the sheet openings 18, in which casethe diameter of the patterned openings will be uniform throughout thedepth of the openings.

The acoustical tile of the present invention also incorporates manyadditional advantageous features. For example the instant tileconstruction obviates many disadvantages considered to be inherent infiber or composition type acoustical boards. Such disadvantages includethe tendency of fibre boards to readily absorb moisture when beingcleaned or painted and their lack of fire resistance (thereby requiringuse restrictions under many building codes). In addition the fibrousmake-up of such tiles does not permit clean, well defiined recesses tobe formed in them (particularly where twist drills are used for thisoperation), i.e. stray loose fibers frequently extend into the recessesfrom the surrounding board leaving the edges of the recesses frayed andincreasing the tendency of paint to bridge over and entirely orpartially clog the recesses. All of these disadvantages are overcome bythe instant tile construction which provides an impervious facing 11making possible ready cleaning or painting of the tile withoutabsorption of liquid into the porous backing board, as well as providingwell defined openings 13 which reduce the tendency of paint to bridgeover and clog the board recesses 15. The metal or plastic facing 11 alsoincreases the fire resistance of the tile and makes it available formore applications.

In the illustrated embodiment, the recesses 15 and openings 18 have beenshown to be of various sizes and arranged in a random pattern across theface of the tile 11) (see FIG. 1), It is to be understood, of course,that other patterns, sizes and shapes of recesses and openings may beemployed if desired. For example another arrangement falling within thescope of the present invention would be one in which the recesses andopenings are uniformly sized and spaced.

We claim as our invention:

1. An acoustical tile for absorbing sound vibrations comprising, incombination, a substantially rigid backing member formed of a soundabsorbing material of a relatively light weight porous nature, saidbacking member defining a pattern of spaced cylindrical recessesextending substantially into said backing member and terminated by abase port-ion formed internally of said backing member for dispersingsound vibrations within the backing member, a facing sheet having aseries of openings distributed over its face in a pattern correspondingto that of said recesses, said facing sheet overlying and in contactwith said backing member such that said openings are in registry withsaid recesses, and said facing sheet having portions thereof marginal tosaid openings smoothly rounded out of the plane of the facing sheet andinto the recesses of the backing member to thereby form an inturned liparound each opening, each of said inturned lips having a smallertransverse dimension than said recesses cooperating therewith to form acaptive corner behind said facing sheet to trap sound vibrations withinsaid recesses.

2. An acoustical tile as defined in claim 1 wherein said openings arecircular and said inturned lips are circumferentially disposed and theratio of the diameters of said cylindrical recesses to the diameters ofsaid openings References Cited by the Examiner UNITED STATES PATENTSHoward 18133 Smith 181--33 Burgess 181-33 Lambert 15444.5 Hudson 154-445Newport et a1. 181--33 Brisley et a1. 15444 Schulz 181--33 GreatBritain.

at the innermost end of said lips is in the range of from 15 LEO SMILOWElma? Exami'ler- C. F. KRAFFT, Examiner.

about 1.25 to about 3.33.

1. AN ACOUSTICAL TILE FOR ABSORBING SOUND VIBRATIONS COMPRISING, INCOMBINATION, A SUBSTANTIALLY RIGID BACKING MEMBER FORMED OF A SOUNDABSORBING MATERIAL OF A RELATIVELY LIGHT WEIGHT POROUS NATURE, SAIDBACKING MEMBER DEFINING A PATTERN OF SPACED CYLINDRICAL RECESSESEXTENDING SUBSTANTIALLY INTOI SAID BACKING MEMBER AND TERMINATED BY ABASE PORTION FORMED INTERNALLY OF SAID BACKING MEMBER FOR DISPERSINGSOUND VIBRATIONS WITHIN THE BACKING MEMBER, A FACING SHEET HAVING ASERIES OF OPENINGS DISTRIBUTED OVER ITS FACE IN A PATTERN CORRESPONDINGTO THAT OF SAID RECESSES, SAID FACING SHEET OVERLYING AND IN CONTACTWITH SAID BACKING MEMBER SUCH THAT SAID OPENINGS ARE IN REGISTRY WITHSAID RECESSES, AND SAID FACING SHEET HAVING PORTIONS THEREOF MARGINAL TOSAID OPENINGS SMOOTHLY ROUNDED OUT OF THE PLANE OF THE FACING SHEET ANDINTO THE RECESSES OF THE BACKING MEMBER TO THEREBY FORM AN INTURNED LIPAROUND EACH OPENING, EACH OF SAID INTURNED LIPS HAVING A SMALLERTRANSVERSE DIMENSION THAN SAID RECESSES COOPERATING THEREWITH TO FORM ACAPTIVE CORNER BEHIND SAID FACING SHEET TO TRAP SOUND VIBRATIONS WITHINSAID RECESSES.